Mechanisms of polystyrene microplastic degradation by the microbially driven Fenton reaction

Abstract

Natural hydroxyl radical (·OH) production, which partially occurs through the microbially driven Fenton reaction, can enhance the degradation of polystyrene microplastics (PS-MPs). However, ·OH causes damage to microorganisms, which might in turn restrain the microbially driven Fenton reaction. Thus, whether PS-MPs can be continuously degraded by the microbially driven Fenton reaction and how they are degraded are still unknown. A pure-culture system using Shewanella putrefaciens 200 was set up to explore the effect and mechanism of microbially driven Fenton reaction on PS-MP degradation. In a 14-day operation, ·OH produced by the microbially driven Fenton reaction could degrade PS-MPs with a weight loss of 6.1 ± 0.6% and an O/C ratio of 0.6 (v.s. 0.6 ± 0.1% and 0.1, respectively, in the ·OH quenched group). Benzene ring derivatives such as 2-isopropyl-5-methyl-1-heptanol and nonahexacontanoic acid were the main soluble products of PS-MP degradation. The ·OH-induced oxidative damage on microorganisms did not affect ·OH production significantly when there was timely replenishment of organic carbon sources to promote reproduction of microorganisms. Thus, PS-MPs can be continuously degraded by microbially driven Fenton reactions in natural alternating anaerobic-aerobic environments. This study also provides a new microbial technique for MP degradation that is different from previous technologies based on microbial plastic-degrading enzymes.

Keywords: Fenton reaction; Hydroxyl radical; Iron-reducing bacterium; Microbial damage; Polystyrene microplastic.